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5 Y 2 If hydrocarbon odors or signs of hydrocarbon are detected in a soil sample, selected soil samples will be analyzed for benzene, toluene, abd xylene (BTX) by U.S. Environmental Protection Agency (EPA) Method 8020, for total petroleum fuel hydrocarbons by EPA Method 8015 modified, and for total lead. The samples will be delivered to BC ' s analytical laboratory in Emeryville within 48 hours of collection. Groundwater Monitoring Wells During monitoring well installation, development, and sampling, the following procedures will be used . These methods will ensure the proper identification of groundwater quality beneath the site. Groundwater Monitoring Well Installation. At least three groundwater monitoring wells will be installed. Three groundwater monitoring wells are required to correctly determine groundwater gradient and flow direction. The wells will be completed with 2-inch-diameter polyvinyl chloride (PVC) flush-threaded casing and will be screened with 0, 020-inch slotted casing from 20 feet below the groundwater surface to 2 feet above the groundwater surface. Blank casing will extend from the top of the perforated section to ground surface. Actual depths of the boreholes and screened intervals will depend on the conditions encountered during drilling . The wells will be packed with No. 20/40 sand or equivalent from the bottom of the screen to approximately 2 feet above the top of the screen. A 2--foot seal of bentonite pellets will be placed on the top of the sand pack. The wells will be grouted with bentonite-cement slurry or neat cement from the top of the bentonite seal to the surface . The wells will be completed below grade , fitted with top and bottom PVC caps, and have water-tight locking covers installed. Typical well construction is illustrated on Figure 1. The monitoring wells will not be completed opposite significant clay zones nor will monitoring wells penetrate significant clay zones whose penetration might allow for downward migration of contamination into lower aquifers. Well Develo ment and Groundwater Samples. Each well installed will be developed by surging and bailing until clean , sediment--free water is produced from the well . The length of development time will vary depending upon field conditions. Water produced during development and sampling will be contained on site . ARCO will be responsible for the disposal of water and product collected. Prior to and following development, the thickness of free product, if any, will be gauged .